Apparatus for the uniform preparation of silver halide grains

ABSTRACT

An apparatus for its practice are disclosed where, uniformly sized silver halide grains are precipitated in an aqueous peptizer solution by the reaction of a silver salt solution with a halide salt solution, where at least one of the solutions has been mixed with a portion of the peptizer solution prior to its reaction with the other solution within the remainder of the peptizer solution. Apparatus is disclosed for practicing the method of this invention including at least one separate mixing chamber for dilution of a salt solution with a portion of the peptizer solution prior to the precipitation reaction.

nited States Porter et a1.

[ APPARATUS FOR THE UNHFORM PREPARATION OF SILVER HALHDE GRAINS [75]Inventors: Henry 1). Porter; Benjamin A.

Johnson, both of Rochester, NY.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

22 Filed: Nov. 1', 1971 211 App1.No.:194,466

Related US. Application Data [62] Division of Ser. -No. 876,893, Nov.14, 1969,

[ 1 ,Ean. 115, 1974 Primary ExaminerNorman Yudkoff Assistant ExaminerS.J. Emery Atlorney-W. H. .l. Kline et a1.

[57] ABSTRACT An apparatus for its practice are disclosed where,uniformly sized silver halide grains are precipitated in an aqueouspeptizer solution by the reaction of a silver salt solution with ahalide salt solution, where at least one of the solutions'has been mixedwith a portion of the peptizer solution prior to its reaction with theother solution within the remainder of the peptizer solution. Apparatusis disclosed for practicing the method of this invention including atleast one separate mixing chamber for dilution of a salt solution with aportion of the peptizersolution prior to the precipitation reaction.

4 Claims, 6 Drawing Figures PMENIEDJAN 1 4 .3; 785,77?

SHEET 1 BF 2 This application is a division of U. S. application Ser.No. 876,893, filed Nov. 14, 1969, now abandoned. This invention relatesto apparatus for the preparation of silver halide crystals.

In the preparation of silver halide type photographic emulsions it isoften desirable that the silver halide crystals or grains used thereinbe in a finely divided form. Preparation of finely divided silver halidehas normally been accomplished by the precipitation of the silver halidegrains by means of a so-called double decomposition reaction in anaqueous solution of a colloidal, aqueous peptizer solution, for example,an aqueous gelatin solution. Two convenient methods for performing thedouble decomposition reaction are characterized by the manner ofintroduction of the reactants, i.e., by single jet or double jet means.A thorough discussion of these methods of reaction can be found in thefollowing references: PHOTOGRAPHIC CHEMIS- TRY, Pierre Glafkides,Fountain Press, London, 1958, pp. 327-330; NUCLEATION IN SILVER BROMIDEPRECIPITATION, C. R. Berry and 'l). C. Skillman, J. Phys. Chem., 68,1138-43 (1964); and THE THEORY OF THE PI-IOTOGRAPHIC PROCESS, ThirdEdition, C.E.K. Mees and T. H. James MacMillan, 1966, Chapter 2, page34. Emulsions made by these techniques are now referred to as single jetor double jet emulsions.

In preparing a typical double jet emulsion, an aqueous solution of awater soluble silver salt and an aqueous solution of a water solublehalide are added simultaneously to the aqueous peptizer solution. As theresultant silver halide grains are precipitated, the individual grainsize normally tends to vary widely, particularly during the preparationof fine grain emulsions. In general, nonuniformity in the size of theprecipitated silver halide grains caused by aggregation of grains andthe like imparts adverse photographic characteristics to thephotographic'materials produced therefrom. For example, clumped oraggregate crystals tend to develop spontaneously causing an undesirablephenomenon known as pepper fog. Typical emulsions prepared with silverhalide grains precipitated bythe single jet method can likewise exhibitthe aforementioned adverse characteristics.

There have been several attempts to produce silver halide grains havinga narrow grain size distribution, i.e., a substantially uniform sizethroughout. Specifically, emulsions have been prepared which containsubstantially fewer non-uniform large grains than were possible with theolder precipitation techniques. Exem plary of the improvements'in silverhalide precipitation techniques are US. Pat. No. 2,996,287 and U.S. Pat.No. 3,415,650. These patents, respectively, disclose an apparatus andthe method for improving the dispersion of a salt solution into apeptizer solution and a method of removing reaction product from areaction zone so as to diminish the possibilities for crystal aggregateformation.

While the aforementioned apparatus and method were achievements inovercoming some of the drawbacks related to double jet and single jetprecipitations, limitations in these methods have produced problems. Forexample, it is not possible to achieve greater production from existingapparatus by increasing the concentration of the reactants withoutincreasing the resultant grain size distribution and thereby producingpepper fog.

Fine grain photographic emulsions containing silver halide grainsprepared according to the method and apparatus of this invention, aresubstantially free of nonuniform large grains and the resultant productis free of pepper fog. Such emulsions exhibit better high light contrastand sharpness than heretofore. These characteristics are particularlydesirable in multicolor materials where local ill effects from aggregategrains are damaging to image quality.

Production of coarser grain emulsions, particularly of the single jettype are also improved by the method of this invention. Greaterconcentrations of reactants can be handled in emulsion preparation whileexperiencing a substantial reduction in the population of aggregategrains produced.

The aforementioned advantages have been achieved, i.e., non-uniformgrain formation has been substantially eliminated, according to themethod of the present invention when preparing emulsions with silverhalide grains in the size range of from 0.1 micron to 5 microns by firstmixing at least one of the aqueous salt solutions with a portion of theaqueous peptizer solution while isolated therefrom, and then introducingthe peptizerdiluted salt solution into the remainder of the peptizersolution. A sufficient concentration of silver salt and halide salt isthen provided by continued addition to the recirculatedpeptizer'solution in the same manner to produce the desired silverhalide grain formation.

The method of this invention is preferably carried out in the followingmanner to predictably form uniformly sized silver halide grains for adouble jet emulsion.

First an aqueous silver salt solution is diluted with a portion of agelatin peptizer solution, simultaneously an aqueous solution of ahalide salt is diluted with a separate portion of the peptizer solutionwhile isolated from the diluted silver salt and both are isolatedinitially from the remainder of the pepetizer solution. The twoseparately diluted portions are then introduced into the remainder ofthe peptizer solution preferably at a point below the surface thereofand in such a manner that the diluted solutions are substantiallyseparate from each other until they are brought into reacting contactwithin the bulk of the pepetizer solution. By this method the formationof uniform grain size from concentrated salt solutions is substantiallyenhanced. The reaction is continued by recirculation of portions ofpeptizer-product slurry by means of the apparatus of this invention toseparately dilute the silver salt and halide salt solutionsbefore'introduction of the reactants into the bulk of thepeptizer-product mix, preferably in contiguous streams.

The above as well as further advantages of the present invention will bemore completely understood from the following description of preferredapparatus for practicing the herein described method. Reference is madeto the drawings wherein:

FIG. 1 is a side elevation partly in section of a mixing apparatusaccording to the present invention.

FIG. 2 is a partially sectioned view of the top of the mixing chambershown in FIG. I.

FIG. 3 is a sectional view taken along the lines and arrows 3-3 of FIG.2.

FIG. 4 is a side elevation partially in section of another mixingapparatus embodiment of the present invention.

FIG. 5 is a partially sectioned view of the top of the mixing chambershown in FIG. 4.

FIG. 6 is a sectional view taken along the lines and arrows of FIG. 5. I

Referring now to the embodiment of this invention shown in FIGS. 1, 2and 3, it will be seen that a centrif ugal mixing device 10 is providedwhich includes a rotatably mounted shaft 12, connected to an electricmotor 14. The motor is mounted on a bracket 16 which is attached in asuitable manner to the mixing tank or vessel 20. The mixing device 10 isfurther provided with a housing 18 which is rigidly supported by rod 22to the motor bracket 16. The housing 18 is provided at its top withinlet pipes 24 and at its bottom with inlet pipes 26 which communicatewith the interior of housing 18. Outlet ports 28 provided with baffles30, located in spaced relationship generally around the middlecircumference of housing 18.

The interior of mixing device 10 is shown in detail in FIG. 3. A doubleconically shaped mixing head 36 is attached to shaft 12 and is providedwith an upper portion 38 which slopes inwardly above the supporting ring34 and is provided with exit slots 40 and interior baffles 42. Likewise,the bottom portion 44 of mixing head 36 is similarly provided with slots40 and baffles 42. Support ring 34 is a flat solid, non-perforated diskseparating the upper portion 38 from the lower portion 44 and isdisposed within the housing 18 in a position to roughly divide thehousing into two halves, the intersections of two halves being roughlyprovided to coincide with the outlet ports 28.

FIG. 2 is a top view of the circular housing 18 showing the approximatelocationof slots 40, baffle plates 42 and the annular opening 46 aroundthe shaft 12 into which the inlet pipes 24 empty.

It can be seen from an inspection of the mixing device 10, thatreactants, such as an aqueous silver salt solution and an aqueous halidesolution, can be introduced alternatively through either top pipes 24 orbottom pipes 26, respectively, from where they will enter by the actionof rotation of the mixing head into the zone defined by the support ring34 and the upper half or lower half of housing 18. Adjustment of thesize of the annular opening 46 around shaft permits introduction of aportion of the bulk peptizer solution into the housing 18 under theinfluence of the rotating mixing head 36 with its baffles 42, and ports40. In this manner the aqueous silver solution is premixed in one halfof the housing 18 with a portion of the bulk peptizer solution whilehalide salt solution is premixed in another portion of the housing 18with a separate portion of the bulk peptizer solution. Both predilutedreaction streams are then forceably ejected through outlet ports 28 bythe centrifugal force applied by the mixing head 36 and directed deepinto the bulk of the remaining peptizer solution by baffles 30. It isdemonstrated hereinafter that separate premixing of a portion of thepeptizer solution with each of the reactants and subsequent contiguousejection of the diluted reactants permits the successful handling ofhigher concentrations then previously possible of each of the reactantsdescribed hereinbefore. This is accomplished simultaneously with theprevention of aggregate silver halide crystal formation within the bulkof the peptizer solution as the reactants come together and silverhalide is precipitated within the vessel 20. At the required time thevessel may be evacuated by means of the open end provided at 48 in FIG.1.

Dilution of fresh salt solution is also possible using recirculatedpeptizer-product slurry until the optimum time of run is achieved. Thefeed of reactants and peptizer to the mixing chambers can be by actionof the mixing head as disclosed or by the use of supplemental equipmentsuch as pumps where necessary. Likewise the optimum size for openingsand pipes as well as their placement may vary from those shown wheredesign changes are effected.

Another mixing apparatus embodiment of the present invention is shown inFIGS. 4, 5 and 6. The structure for this mixing apparatus is similar tothat shown in FIGS. 1, 2 and 3 in that the'mixing device 60 hasprotruding through the top thereof, the shaft 62 connected to a motor 64which is attached to the top of the mixing tank or vessel by means of abracket 66. The housing 68 of the mixing device 60 is supported beneaththe liquid level of the fluid in vessel 70 by means of a supporting rod72.

The housing 68 is provided at its top with inlet ports 24 and at itsbottom with inlet ports 26. Outlet ports 78 are located generally aroundthe middle periphery of housing 68.

The interior of mixing device 60 is shown in detail in FIG. 6. A twozone mixing head 86 is attached to shaft 62 and is provided with anupper zone containing perforated mixing vanes 87 attached to shaft 62and a lower zone with similar perforated mixing vanes 87. The vanes 87in both zones may also be attached to support plate 34. Support plate 34is a flat solid disk separating the upper zone from the lower zone andis disposed within the housing 68 in a position which roughly dividesthe housing into two halves, the intersections of the two halves roughlycoincides with the middle of outlet ports 78.

FIG. 5 is a top view of the generally square housing 68 showing theapproximate location of the outlet ports 78 and the annular opening 46around the shaft 62 into which the inlet pipes 24 empty.

The invention is further illustrated by reference to the followingexamples of preferred embodiments thereof. It should be understood thatthese examples are included for purposes of illustration and thatspecific amounts, techniques and the like are not intended to beconstrued as limiting in any manner the scope of the invention asdisclosed hereinbefore.

EXAMPLE I A single jet silver bromoiodide gelatin emulsion containing 6mole percent iodide is prepared in the following manner. Aqueous halidegelatin solution containing 76.8 grams of potassium iodide and 866 gramsof potassium bromide is adjusted to a total volume of 242 ounces andthereafter maintained at F. throughout the precipitation reaction. Anamount of silver nitrate, 1,188 grams, is then dissolved in a totalvolume of I82 ounces of distilled water. This volume is introduced intothe mixing chamber of FIG. 1 over a period of 20 minutes while thechamber is located below the surface of the previously prepared aqueoushalide gelatin solution, and while the motor 14 is operating the mixingdevice 10. The resultant emulsion is washed by the coagulation proceduredescribed in Yutzy et al. U.S. Pat. No.

2,614,968. An aqueous gelatin solution is added to the washed coagulantresulting from the coagulaton procedure in order to obtain the desiredconsistency. The total gelatin emulsion is then dispersed at 104F. and apH of 6.4. After dispersion the emulsion is sulfur and gold sensitizedby conventional techniques and then heated for several minutes at 150F.,cooled to 104F. and coated, with appropriate couplers, spreading andhardening agents onto a cellulose acetate support.

For comparison with theforegoing, an aqueous gelatin solution containing433 grams of potassium bromide and 38.4 grams of potassium iodide isadjusted to a total volume 182 ounces. A halide gelatin solution is thenheated to 151F. and held at that temperature throughout theprecipitation. An amount of silver nitrate, 594 grams, is dissolved inenough distilled water to make a total volume of 225 ounces. This silvernitrate solution is then added to the surface of the halide gelatinsolution over a period of 40 minutes while the halide gelatin mixture isstirred vigorously with conventional motor driven stirrers. Thisemulsion is likewise washed by the coagulation procedure identifiedhereinbefore and additional aqueous gelatin solution is added to thewashed coagulant to obtain the desired consistency and the gelatinemulsion is thendispersed at 104F. and a pH of 6.4. This emulsion isalso sulfur and gold sensitized in a conventional manner, heated forseveral minutes at 150F., cooled to 104F., and then coated withappropriate couplers, spreading and hardening agents onto a celluloseacetate support.

Coatings prepared as hereinbefore described were exposed on anintensityscale sensitometer for onetenth of a second at 2,8S1(., identicallydeveloped, washed and dried in the conventional manner to produce thefollowing tabular results.

Coating Relative Number Gamma Dmax Dmin Speed l 4.1 2.38 0.09 100 It canbe seen from the above table that the emulsion EXAMPLE 2 A coarse grainsilver bromoiodide gelatin emulsion containing 6 mole percent iodide isprepared according to the present invention using the agitator shown inFIG. 4. The aqueous halide gelatin solution containing 19.6 grams ofpotassium iodide and 922 grams of potassium bromide is adjusted to atotal volume of 225 ounces. This solution is held at 135F. throughoutthe precipitation. A quantity of silver nitrate, 1,188 grams, is thendissolved in an aqueous solution having a total volume of 166 ounces.The reactant is introduced into a gelatin solution below its surface bymeans of a separate mixing chamber shown in FIG. 4 until the elapsedtime of premixing and introduction into the gelatin is 20 minutes. Theresultant emulsion is then washed by the coagulation procedure describedin Yutzy et a1.

U.S. Pat. No. 2,614,968. Additional aqueous gelatin solution is added tothe washed coagulant to obtain the desired consistency and the resultantemulsion is dispersed at 104F. and a pH of 6.4. This emulsion is sulfurand gold sensitized in the conventional manner and heated for severalminutes at 150F., cooled to 104F. and coated with appropriate spreadingand hardening agents on a cellulose acetate support.

For comparison, an aqueous gelatin solutioncontaining 461 grams ofpotassium bromide and 9.8 grams of potassium iodide is adjusted to atotal volume of 186 ounces. A separate aequeous solution containing 594grams of silver nitrate is adjusted to a total volume of 255 ounces.Silver solution is then added to the gelatin solution which ismaintained at a temperature of 144F. The addition lasts 40 minutes. Thegelatin mixture is stirred throughout with a conventional motor-drivenpropeller mounted on the end of a shaft. The emulsion was washed by thecoagulation procedure described hereinbefore and coated in the samemanner. Samples of each coating are exposed on an intensity scalesensitometer for one-tenth of a second at 2,850K., developed in theconventional manner, washed and dried with the following results.

Coating v Gamma Dmax Dmin Relative Speed It can be seen from the abovetables that the emulsion from the first run prepared by the method andapparatus of the present invention using less time and lower temperatureand with increased concentration of reactants than the second run,exhibits photographic results equal to the emulsion of the second runwhich is prepared by conventional methods.

EXAMPLE 3 Two separate double jet chlorobromide (80:20) gelatinemulsions are prepared in a manner similar to the hereinbefore describedmethods except for the following: Emulsion A was prepared in a mannersuch that the silver nitrate solution and the aqueous mixture ofpotassium bromide and potassium chloride are allowed to run onto thesurface of the gelatin solution. A wide silver halide grain sizedistribution is obtained with this method.

Emulsion B is prepared in a manner such that the silver nitrate solutionand the halide solution entered the feed tubes of the mixing deviceshown in FIG. 1. More uniform silver halide grains obtained by themethod and apparatus of the present invention.

EXAMPLE 4 A single jet coarse grain silver bromoiodide gelatin emulsioncontaining 6 mole percent iodide is prepared in a conventionalmanner (asdescribed in Example 1), except for the following changes. An aqueousgelatin solution containing 866 g. of potassium bromide and 76.8 g. ofpotassium iodide is adjusted to a total volume of 90 ounces. Silvernitrate (1,188 g.) is dissolved in enough distilled water to make atotal volume of 90 ounces and added to the surface of the halide gelatinsolution over a period of 40 minutes.

The results of the above emulsion, after coating and processing asdescribed in Example 1, displayed a high level of fog which appears onthe processed print as pepper fog.

An emulsion was prepared using the concentrations previously describedin this example and the agitating device as shown in FIG. 3. Only onechamber of the mixer is used. The silver halide grains, as shown in FIG.l illustrate substantially no silver halide aggregates.

The results, after processing as described in Example 1, shows noappreciable fog.

Apparatus simlar to FIGS. 1, 2 and 3 employing half of the mixing headare useful in preparing single jet type emulsions. Likewise, the entiremixing head can be used for single jet type emulsions where both top andbottom inlet pipes feed the same reactant.

1n the method of precipitating silver halide crystals according to thepresent invention it is advantageous for the pAg and/or pH of thepeptizer-silver halide mixture to be continuously monitored andcontrolled by the proportional addition generally as hereinbeforedescribed of silver salt solutions and/or halide salt solutions inresponse to changes in pAg. Exemplary of pAg control means are thedisclosures in U.S. Pat. No. 3,031,304 and U.S. Application Ser. No.699,616 filed Jan. 1, 1968 (Belgian Patent 727,189). likewise, thearticle by F. H. Claus and W. Pellaers, Crystal Habit Modification ofAgBr by Incorporation of l-Ions, Photographische Korrespondez 103. Band,1967, discloses useful control means. Such control can be carried out inan interrupted manner, a continuous manner or a semi-continuous mannerconsistent with the total precipitation procedure ofthe presentinvention. The pAg of the system can be determined by methods commonlyused in the trade and is mathematically expressed as the negativelogarithm of the silver ion concentration in moles per liter. The pAg isconventionally obtained by measuring the difference between a referenceelectrode and a so-called pAg electrode which can be a silver electrode.

The silver halide emulsions which can be made from silver halideprepared according to this invention include silver chloride, silverbromide, silver bromoiodide, silver chlorobromoiodide, or mixturesthereof. The emulsions may be coarse or fine grain such as fine grainedsilver chlorobromide emulsions and fine grained monodispersed silverhalide emulsions of the type described in lllingsworth U.S. ApplicationSer. No. 500,366 (French Pat. No. 1,497,202 issued Aug. 28, 1967). Theseemulsions can be prepared by any of the well-known procedures, e.g.,single jet emulsions, double jet emulsions, such as Lippman emulsions,ammoniacal emulsions, thiocyanate or thioether ripened emulsions such asthose described -in Nietz et al., U.S. Pat. No. 2,222,264, lllingsworth,U.S. Pat. No. 3,320,069, and McBride, U.S. Pat. No. 3,271,157. Surfaceimage emulsions may be used or internal image emulsions such as thosedescribed in Davey et al, U.S. Pat. No. 2,592,250; Lowe et al., U.S.Pat. No. 3,206,313; Berriman et al., U.S. Pat. No. 3,367,778 and Baconet al. Belgian Pat. No. 704,255, as well as buried iodide emulsions ofthe type described in Porter et al. U.S. Application Ser. No. 648,225(Belgian Pat. No. 716,914 issued Aug. 31, 1968). lfdesired, mixtures ofsurface and internal image emulsions may be used as described in Luckeyet al. U.S. Pat. No. 2,996,382. Negative type emulsions may be used ordirect positive emulsions such as those described in Leermakers U.S.Pat. No. 2,184,013; Kendall et al., U.S. Pat. No. 2,541,472; Berriman,U.S. Pat. No. 3,367,778; Schouivenaars British Pat. No. 723,019;lllingsworth French Pat. No. 1,520,821; lves U.S. Pat. No. 2,563,785;Knott et al. U.S. Pat. No. 2,456,953 and Land U.S. Pat. No. 2,861,885.

The silver halide emulsions used with this invention may be unwashed orwashed to remove soluble salts. 1n the latter case the soluble salts maybe removed by chill-setting and leaching or the emulsion may becoagulation washed, e.g., by the procedure described in Hewitson et al.U.S. Pat. No. 2,618,556; Yutzy et al. U.S. Pat. No. 2,614,928; YackelU.S. Pat. No. 2,565,418; Hart et al. U.S. Pat. No. 3,241,969; and Walleret al., U.S. Pat. No. 2,489,341.

The emulsions used with this invention may likewise be sensitized withchemical sensitizers, such as with reducing agents; sulfur, selenium ortellurium compounds; gold, platinum or palladium compounds; orcombinations of these. Suitable procedures are described in Shepard U.S.Pat. No. 1,623,499; Allen U.S. Pat. No. 2,399,083; McVeigh U.S. Pat. No.3,297,447; and Dunn U.S. Pat. No. 3,297,446.

This invention may be used to produce elements designed for colorphotography, for example, elements containing color-forming couplerssuch as those described in Frohlich et al. U.S. Pat. No. 2,376,679;Vittum et al. U.S. Pat. No. 2,322,027; Fierke et al. U.S. Pat. No.2,801,171; Godowsky U.S. Pat. No. 2,698,794; Barr et al. U.Sv Pat. No.3,227,554 and Graham U.S. Pat. No. 3,046,129; or elements to bedeveloped in solutions containing color-forming couplers such as thosedescribed in Marines and Godowsky U.S. Pat. No. 2,252,718; Carroll etal. U.S. Pat. No. 2,592,243 and Schwan U.S. Pat. No. 2,950,970.

Further the emulsions capable of being prepared are useful in thepreparation of multilayer photographic elements which may beorthosensitized or pan-sensitized with spectral sensitizing dyes. Forinstance, these emulsions can be spectrally sensitized by treating witha solution of a sensitizing dye in an organic solvent or the dye may beadded in the form of a dispersion as described in Owens et al. FrenchPat. No. 1,482,774. Sensitizing dyes useful in sensitizing suchemulsions are described, for example, in US. Pat. Nos. 2,526,632 ofBrooker and White issued Oct. 24, 1950; 2,503,776 of Sprague issued Apr.11, 1950; Brooker et al. U.S. Pat. No. 2,493,748 and Taber et al. U.S.Pat. No. 3,384,486. Spectral sensitizers which can be used include thecyanines, merocyanines, complex(trinuclear) cyanines,complex(trinuclear) merocyanines, styryls and hemicyanines. The cyaninesmay contain such basic nuclei as thiazoles, oxazoles, selenazoles,imidazoles. Such nuclei may contain sulfoalkyl; carboxyalkyl andalkylamino groups and may be fused to benzene or naphthalane ringseither unsubstituted or substitued with halogen, phenyl, alkyl or alkoxygroups. The dyes may be symmetrical or unsymmetrical and may containalkyl, phenyl or heterocyclic substituents on the polymethine chain. Themerocyanine dyes may contain the basic nuclei mentioned above as well asacid nuclei such as thiohydantoins, rhodanines, oxazolidenedienes andbarbituric acids. The acid nuclei may be substituted with alkyl groups,phenyl groups, carboxy, sulfo,

or amino groups. The emulsions may contain supersensitizing dyecombinations such as those described in Brooker et a1. U.S. Pat. No.2,739,964; Carroll et al. U.S. Pat. No. 2,688,545; Carroll et al. U.S.Pat. No. 2,701 ,198; VanLare U.S. Pat. No. 2,739,149; Fuji British Pat.No. 1,128,840 or the dyes may be supersenzitized with ascorbic acidderivatives, azaindenes, cadmium salts, and organic sulfonic acids asdescribed in McFall et al. US. Pat. No. 2,933,390 and Jones et al. U.S.Pat. No. 2,937,089.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. An apparatus submergible in the bulk of a first solution forseparately diluting each of a second solution and a third solution witha portion of the first solution and for mixing the diluted second andthird solutions in the bulk of the first solution, comprising:

a generally hollow housing having a longitudinal axis and provided witha plurality of outlet ports arranged equiangularly relative to the axisand radially aligned with a horizontal plane substantially perpendicularto said axis and midway between the ends of the housing, a vane fixed toand extending outwardly from the outer surface of the housing adjacenteach of the outlet ports, and a central inlet port in each end of thehousing through which the first solution can flow into the housing;

mixing means mounted in the housing and rotatable about the axis, saidmixing means including an imperforate plate dividing the housing intotwo chambers at the central horizontal plane and filling a large portionof the cross-sectional area of the housing, and at least one mixingelement associated with each side of the plate;

first conduit means operatively connected to the one end of the housingfor introducing the second solution into the one chamber;

second conduit means operatively connected to the other end of thehousing for introducing the third solution into the other chamber; and

means coupled to the mixing means for rotating the latter, whereby uponsubmergence the first solution is drawn into each chamber to separatelyform the second and third diluted solutions, the latter solutions beingseparately mixed and radially ejected from their respective chamberthrough the outlet ports as contiguous streams into the bulk of thefirst solution, the contiguous streams and vanes agitating the firstsolution so as to intermix the diluted solutions therein.

2. Apparatus in accordance with claim 1 wherein the mixing elementcomprises a hollow, truncated conical member fixed to the one side ofthe plate and having an open end opposite the plate, a plurality ofelongated openings in the lateral portion thereof and a plurality ofradial vanes within the member.

3. Apparatus'in accordance with claim 1 wherein the mixing elementcomprises a plurality of radially extending, perforated plates fixed toand normal to the imperforate plate.

4. Apparatus in accordance with claim 1 wherein the first solutioncomprises a peptizer solution and the second and third solutionscomprise silver and halide salt solutions for mixing dilutions of thelatter with the peptizer to form silver halide grains.

2. Apparatus in accordance with claim 1 wherein the mixing elementcomprises a hollow, truncated conical member fixed to the one side ofthe plate and having an open end opposite the plate, a plurality ofelongated openings in the lateral portion thereof and a plurality ofradial vanes within the member.
 3. Apparatus in accordance with claim 1wherein the mixing element comprises a plurality of radially extending,perforated plates fixed to and normal to the imperforate plate. 4.Apparatus in accordance with claim 1 wherein the first solutioncomprises a peptizer solution and the second and third solutionscomprise silver and halide salt solutions for mixing dilutions of thelatter with the peptizer to form silver halide grains.